TWI761616B - The production method of hexafluorobutadiene - Google Patents

Abstract

will contain hexafluorobutadiene and at least one selected from the group consisting of octafluoro-1-butene, octafluoro-2-butene, heptafluoro-1-butene and heptafluoro-2-butene The raw material composition of the additional compound is subjected to extractive distillation in the presence of an extraction solvent to reduce the concentration of the aforementioned additional compound, thereby obtaining higher purity hexafluorobutadiene.

Description

Manufacturing method of hexafluorobutadiene

The present invention relates to a method for producing hexafluorobutadiene.

At present, the miniaturization of semiconductor devices for high speed and power saving and the utilization of novel materials are being considered. Fluorocarbons are known to be suitable for the microfabrication of semiconductor devices, among them also hexafluorobutadiene (also known as _CF2 =CFCF= _CF2 , 1,1,2,3,4,4-hexafluorobutadiene). ene, etc.) has attracted attention as an etching gas for forming state-of-the-art microstructures such as semiconductors and liquid crystals.

In order to improve the yield of dry etching gas, it is necessary to reduce impurities as much as possible. As the purity of the gas generally used in dry etching, high-purity substances called purity 99.99% (4N) and 99.999% (5N) are used, for example. On the other hand, as a method for producing hexafluorobutadiene, for example, a dehalogenation reaction in which a corresponding halide is reacted with metallic zinc is known (for example, refer to Patent Document 1). [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 62-26240

[The problem to be solved by the invention]

However, hexafluorobutadiene purified by the reaction described in Patent Document 1 contains, as additional compounds, octafluoro-1-butene, octafluoro-2-butene, heptafluoro-1-butene, Heptafluoro-2-butene, etc.

Hexafluorobutadiene and the above-mentioned additional compounds are similar in structure and have similar boiling points. Therefore, since separation is difficult by ordinary distillation methods, a method for obtaining high-purity hexafluorobutadiene is required.

The present invention is made to solve the above-mentioned problems, and aims to provide a method for obtaining high-purity hexafluorobutadiene. [Means of Solving Problems]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, the present invention has been completed. The present invention includes the following constitutions. Item 1. A method for producing hexafluorobutadiene comprising the step of extractive distillation of a raw material composition comprising hexafluorobutadiene and an additional compound in the presence of an extraction solvent to reduce the concentration of the additional compound, wherein the additional compound is At least one selected from the group consisting of octafluoro-1-butene, octafluoro-2-butene, heptafluoro-1-butene and heptafluoro-2-butene. Item 2. The production method according to Item 1, wherein the extraction solvent used in the extractive distillation is at least one solvent selected from the group consisting of oxygen-containing hydrocarbons and halogen-containing hydrocarbons. Item 3. Separation of hexafluorobutadiene and one selected from the group consisting of octafluoro-1-butene, octafluoro-2-butene, heptafluoro-1-butene and heptafluoro-2-butene A method of at least one additional compound comprising the step of extractive distillation of a composition containing hexafluorobutadiene and the additional compound in the presence of an extraction solvent. Item 4. The method of Item 3, wherein the aforementioned extraction solvent comprises at least one compound selected from the group consisting of oxygen-containing hydrocarbons and halogen-containing hydrocarbons. Item 5. A composition comprising hexafluorobutadiene and a compound selected from octafluoro-1-butene, octafluoro-2-butene, heptafluoro-1-butene and heptafluoro-2-butene For the composition of at least one additional compound in the group, the total amount of the aforementioned composition is set at 100 mol %, and the content of the aforementioned additional compound is less than 0.1 mol %. Item 6. An azeotropic composition comprising hexafluorobutadiene and a compound selected from octafluoro-1-butene, octafluoro-2-butene, heptafluoro-1-butene and heptafluoro-2-butene At least one additional compound in the group. Item 7. The composition according to Item 5 or 6, which is a composition for etching gas, refrigerant, heat transfer medium, foaming agent or resin monomer. [Inventive effect]

According to the present invention, high-purity hexafluorobutadiene can be obtained.

The present invention is selected from the group consisting of hexafluorobutadiene and heptafluoro-1-butene, octafluoro-2-butene, heptafluoro-1-butene and heptafluoro-2-butene The production method of obtaining a higher concentration of hexafluorobutadiene in the composition of the additional compound of at least one of the additional compounds includes a step of extractive distillation of the composition in the presence of an extraction solvent to reduce the concentration of the additional compound.

Hexafluorobutadiene is structurally similar to the above-mentioned additional compound and has a similar boiling point. Therefore, it is difficult to separate by a general distillation method. For example, octafluoro-1-butene boils at 4°C, octafluoro-2-butene at 1.2°C, and heptafluoro-1-butene at 20°C compared to hexafluorobutadiene at 6°C , Heptafluoro-2-butene is 8 ℃. For the separation of these substances by ordinary distillation, a distillation column having a plurality of stages must be used, and separation is virtually impossible. It is economically inefficient because even in the case of separability large losses are incurred. In contrast to this, in the present invention, the concentration of the additional compound is reduced by extractive distillation, whereby high-concentration hexafluorobutadiene can be obtained.

Raw material composition The raw material composition contains hexafluorobutadiene, and is selected from octafluoro-1-butene (CF ₂ =CFCF ₂ CF ₃ ), octafluoro-2-butene (CF ₃ CF=CFCF ₃ ), heptane Fluoro-1-butene (CF ₂ =CFCF ₂ CF ₂ H, CF ₂ =CFCFHCF ₃ , CF ₂ =CHCF ₂ CF ₃ , CFH=CFCF ₂ CF ₃ , etc.) and heptafluoro-2-butene (CF ₃ CF At least one additional compound selected from the group consisting of =CFCF ₂ H, CF ₃ CF=CHCF ₃ , etc.).

Such a raw material composition can be produced by a method conventionally known as a method for producing hexafluorobutadiene. In addition, other methods can also be used to synthesize.

[式中，X¹ 相同或相異，表示氟原子以外的鹵素原子。X² 表示鹵素原子]。When synthesizing by other methods, for example, it can be synthesized by a method having a reaction step of adding a nitrogen-containing compound to a solution of the compound represented by the general formula (1):

[In the formula, X ¹ are the same or different, and represent a halogen atom other than a fluorine atom. X ² represents a halogen atom].

In the general formula (1), X ¹ is a halogen atom other than a fluorine atom, and examples thereof include a chlorine atom, a bromine atom, an iodine atom, and the like. Among them, a chlorine atom or an iodine atom is preferable from the viewpoint that hexafluorobutadiene can be obtained at a higher yield. In addition, X ¹ may be the same or different.

In the general formula (1), X ² is a halogen atom, and examples thereof include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, and the like. Among them, from the viewpoint that hexafluorobutadiene can be obtained at a higher yield, a fluorine atom or a chlorine atom is preferable, and a chlorine atom is more preferable.

Examples of compounds represented by the general formula (1) that satisfy such conditions include ClCF ₂ -CFCl-CF ₂ -CF ₂ I, ICF ₂ -CF ₂ -CF ₂ -CF ₂ I, and the like, and can be changed from From the viewpoint of obtaining hexafluorobutadiene with high yield, ClCF ₂ -CFCl-CF ₂ -CF ₂ I is preferred.

In this production method, for example, a nitrogen-containing compound (N, Amide compounds such as N-dimethylformamide and N,N-diisopropylformamide; amine compounds such as triethylamine; pyridine, picoline, N-methyl-2-pyrrolidone etc. pyridine compounds; quinoline compounds such as quinoline, methylquinoline, etc.) to carry out the reaction. Although this nitrogen-containing compound also includes a compound that is liquid at room temperature, it is preferable to use it as an additive rather than a solvent (use it in a small amount) from the viewpoint of obtaining hexafluorobutadiene with a higher yield. Other reaction conditions are preferably set appropriately in accordance with conventional methods.

In this way, when hexafluorobutadiene is obtained by the conventional production method or the above-mentioned production method, octafluoro-1-butene (CF 2 =CFCF 2 CF 3 ), octafluoro-2-butene (CF ₂ =CFCF ₂ CF ₃ ), octafluoro-2- Butene ( _CF3CF = _CFCF3 ), heptafluoro- ₁ -butene ( _CF2 = _CFCF2CF2H , _{CF2 = CFCFHCF3} , _{CF2 = CHCF2CF3} , CFH= _CFCF2CF3 , etc.) , Heptafluoro-2-butene (CF ₃ CF=CFCF ₂ H, CF ₃ CF=CHCF ₃ , etc.) and other additional compounds. Since hexafluorobutadiene and these additional compounds have similar boiling points and similar structures, it is difficult to separate them by ordinary distillation or the like. In particular, separation is extremely difficult because hexafluorobutadiene and heptafluoro-2-butene have very close boiling points. The composition ratio of each component is not particularly limited, but when the raw material composition is produced by the conventional production method as described above, the content of each component is 73 to 99.9 mol % based on the entire raw material composition as 100 mol %. The composition of hexafluorobutadiene in mol % and 0.1-27 mol % of additional compounds. This range is preferable as a composition separated by extractive distillation.

Extractive distillation In the present invention, the above-mentioned raw material composition is subjected to extractive distillation. In this way, hexafluorobutadiene is separated from octafluoro-1-butene, octafluoro-2-butene, heptafluoro-1-butene, heptafluoro-2-butene, etc. with similar boiling points, and more High-purity hexafluorobutadiene.

This separation makes it possible to use additional compounds such as octafluoro-1-butene, octafluoro-2-butene, heptafluoro-1-butene, heptafluoro-2-butene, etc. in other reactions. things become possible. As an additional compound, hexafluorobutadiene is also used in various applications such as refrigerants, heat transfer media, foaming agents, resin monomers, etc. Use effectively.

Extractive distillation can be achieved by increasing or decreasing the relative volatility of the two components (hexafluorobutadiene and the additional compound) from 1. At this time, the farther the relative volatility is from 1, the easier it is to separate the hexafluorobutadiene and the additional compound by extractive distillation. Furthermore, when the relative volatility is 1, separation by distillation is impossible since the compositions of the phases are the same.

The relative volatility is defined as the ratio of the equilibrium coefficients of the constituents in the fluid mixture, and when the constituents are hexafluorobutadiene (A) and the additional compound (B), hexafluorobutadiene (A) relative to The relative volatility (A/B) of the additional compound (B) is represented by the following formula.

Relative volatility (A/B)=X/Y X represents relative to A (gas phase mole fraction/liquid phase mole fraction).

Y represents relative to B (gas phase mole fraction/liquid phase mole fraction).

Here, when hexafluorobutadiene is distilled off, the relative volatility is usually in the range of more than 1, and it is particularly preferable to use an extraction solvent having a relative volatility of 1.10 to 2.00. If the relative volatility is greater than 1, separation by distillation becomes possible by increasing the gas phase molar fraction of hexafluorobutadiene and increasing the hexafluorobutadiene in the gas phase.

On the other hand, when the additional compound is distilled off, the relative volatility is preferably in the range of less than 1, and it is particularly preferable to use an extraction solvent of 0.10 to 0.90. When the relative volatility is less than 1, the hexafluorobutadiene in the liquid phase increases due to the increase in the molar fraction of the hexafluorobutadiene in the liquid phase, and the additional compound is distilled out.

In the present invention, it is preferable to use an extraction solvent that can easily separate the hexafluorobutadiene and the additional compound.

In the present invention, as the extraction solvent, oxygen-containing hydrocarbons (alcohols, ketones, ethers, etc.), halogen-containing hydrocarbons, etc. (halogenated saturated hydrocarbons, halogenated unsaturated hydrocarbons, etc.), and the like can be used.

Examples of alcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, and tert-butanol. Among them, methanol and ethanol are preferable from the viewpoint of relative volatility.

As ketones, acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, etc. are mentioned, for example. Among them, from the viewpoint of relative volatility, methyl ethyl ketone is preferred.

Examples of ethers include dialkyl ethers such as dimethyl ether, methyl ethyl ether, and diethyl ether; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and ethylene glycol monoethyl ether. Ethylene glycol monoalkyl ethers such as butyl ether; ethylene glycol dialkyl ethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, etc. From the viewpoint of relative volatility, ethylene glycol monoalkyl ether is preferable, and ethylene glycol monomethyl ether is more preferable.

As a halogenated saturated hydrocarbon, 1, 1, 1- trifluoro- 2, 2- dichloroethane (HCFC-123) etc. are mentioned, for example.

As halogenated unsaturated hydrocarbons, trichloroethylene, tetrachloroethylene (perchloroethylene) etc. are mentioned, for example.

These extraction solvents can be used alone or in a mixture of two or more.

Moreover, in the case of a water-soluble extraction solvent, it can be mixed with water and used as an extraction solvent. For example, an aqueous solution of acetone, methanol, etc. can be used, and the mixing ratio of the organic compound to water is preferably less than 50% by mass of water in the extraction solvent from the viewpoint of extraction efficiency. When the amount of water in the organic compound (solvent) increases, the boiling point of the solvent composition increases, and there are problems in that the energy efficiency deteriorates.

The temperature range of the standard boiling point of the extraction solvent is the temperature difference to the extent that the extraction solvent and the compound to be separated in the present invention can be separated by single distillation, stripping, etc., although generally only a temperature difference of 20°C or more is sufficient. However, since the extraction solvent itself may be decomposed if the standard boiling point is too high, the range of the standard boiling point as the specific extraction solvent is preferably 30~150°C, more preferably 30~80°C.

The amount of the extraction solvent used in the present invention is not particularly limited, and the ratio of the amount of the extraction solvent used relative to the raw material (the composition containing hexafluorobutadiene and the additional compound) is higher (the concentration of the extraction solvent is higher) than From the viewpoint of efficiency, for example, with respect to 1 mol of the raw material (the composition containing hexafluorobutadiene and the additional compound), the extraction solvent is preferably 0.1 to 100 mol, more preferably 0.5 to 50 mol. , 1~20 moles is better.

The separation method of the present invention is, for example, as shown in FIG. 1, although the hexafluorobutadiene can be recovered by introducing a composition F11 containing hexafluorobutadiene and an additional compound into the distillation column T1, and extractive distillation in the distillation column T1. However, a solvent recovery column T2 can also be installed on the downstream side of the distillation column T1 to recover the extraction solvent S14 and reuse it in the distillation column T1 at the same time. In this case, the number of stages of the distillation column T1 and the solvent recovery column T2 can be appropriately selected by examining the relationship between the purity of the distillate component, the recovery rate, and the like in advance. Although FIG. 1 is an example in the case of using an extraction solvent with a relative volatility greater than 1, in the case of using an extraction solvent with a relative volatility of less than 1, only hexafluorobutadiene is recovered or recovered in the distillation column T1. Differences in additional compounds can be performed in the same way.

The operating conditions such as the temperature in each part of the distillation column T1 and the solvent recovery column T2, the supply section of the raw material, and the supply amount of the extraction solvent are not particularly limited, but depend on the performance of the distillation column T1 and the solvent recovery column T2, and the non-processed materials. The content ratio of the hexafluorobutadiene and the additional compound in the (raw material), the type and amount of the extraction solvent used, and the like vary. These conditions can be determined by preliminary experiments. In addition, in order to ensure the stability of the distillation operation, an extraction solvent may be added to the raw material first. The method of the present invention can be carried out in discontinuous operation or continuous operation, and industrially, continuous operation is preferred. In addition, by increasing the theoretical number of stages of the extractive distillation column and actually increasing the number of columns, the distillate component can be further purified. In the recovery stream of the product, a mist eliminator for removing the extraction solvent that may be entrained in a very small amount, and a solvent removal tower filled with adsorbents such as activated carbon, molecular sieves, etc., can also be provided.

The reactor used in the present invention can be suitably made of carbon steel lined with at least one of glass, stainless steel, tetrafluoroethylene resin, chlorotrifluoroethylene resin, difluoroethylene resin, PFA resin, etc. .

In this way, the hexafluorobutadiene composition can further purify the hexafluorobutadiene, whereby it can be obtained that the content of the above-mentioned additional compound is less than 0.1 mol% (especially 0.001-0.05 mol%, further 0.001-0.01 mol%) hexafluorobutadiene composition. The hexafluorobutadiene composition can also be obtained as an azeotrope, or an azeotrope-like composition. For example, the composition composed of hexafluorobutadiene and 0.05 mol% CF ₃ CF=CHCF ₃ (C ₄ F ₇ H) has a gas phase composition and a liquid phase composition under the pressure of 0.05MPaG and 15.7°C. 99.95%.

In this way, the hexafluorobutadiene composition of the present invention can be used in various applications such as refrigerants, heat transfer media, foaming agents, resin monomers, etc. Can also be used effectively. [Example]

Examples are shown below and illustrate the characteristics of the invention. The present invention is not limited to these embodiments.

Reference Example 1 In an eggplant-shaped flask with a condenser connected to a trap cooled to -78°C, 40 g (0.16 mol) of xylene, 7.25 g (0.12 mol) of zinc, and 20 g (0.05 mol) of raw material (ClCF) were added. ₂ CFClCF ₂ CF ₂ I) and heated the internal temperature to 140°C with stirring. After the internal temperature was kept constant, it was refluxed while N,N-dimethylformamide (DMF) was added at a dropping rate of 0.04 mol/hour (0.8 mol per 1 mol of the raw material (ClCF ₂ CFClCF ₂ CF ₂ I) mol/hour) dropwise for 1 hour, stirring while continuing to heat under reflux. After the completion of the reaction, the liquid trapped in the trap was analyzed by gas chromatography. The CF ₂ =CFCF=CF ₂ was 89 mol %, the CF ₂ =CFCF ₂ CF ₂ H was 3 mol %, and other additions were made. Compounds (octafluoro-1-butene, octafluoro-2-butene, heptafluoro-1-butene, heptafluoro-2-butene, etc. other than CF ₂ =CFCF ₂ CF ₂ H) are 8 moles in total %. That is, the content of the additional compound was 11 mol %.

Reference Example 2 The same treatment as Reference Example 1 was carried out except that ICF ₂ CF ₂ CF ₂ CF ₂ I was used as a raw material (substrate) instead of ClCF ₂ CFClCF ₂ CF ₂ I. After the completion of the reaction, the liquid trapped in the trap was analyzed by gas chromatography. The CF ₂ =CFCF=CF ₂ was 73 mol %, the CF ₂ =CFCF ₂ CF ₂ H was 20 mol %, and other additions were made. Compounds (octafluoro-1-butene, octafluoro-2-butene, CF ₂ = CFCF ₂ CF ₂ H other than heptafluoro-1-butene, heptafluoro-2-butene, etc.): 2 mol% , and other by-products are 5 mol%. That is, the content of the additional compound was 22 mol %.

Reference Example 3 To the crude product of hexafluorobutadiene (hereinafter, also referred to as "C ₄ F ₆ ") obtained in Reference Example 1, the following solvent was added to observe by-products (CF ₃ CF=CHCF ₃ , Hereinafter, the concentration change is also indicated as "C ₄ F ₇ H") and the effect as an extraction solvent was confirmed. The results of calculating the relative volatility of hexafluorobutadiene and CF ₃ CF=CHCF ₃ from the results of the gas-liquid equilibrium measurement are shown in Table 1 below. For use as an extraction solvent, the relative volatility must be far from 1. From the results in Table 1, it can be understood that ethylene glycol monomethyl ether, perchloroethylene (tetrachloroethylene), methanol, ethanol and methyl ethyl ketone can be used as extraction solvents, and hexafluorobutanediol can be used as the extraction solvent. High purity of alkene.

Example 1 Simulation evaluations were performed for the separation method of the present invention.

Methanol was used as the extraction solvent, and an extractive distillation process was constructed. Methanol was fed in a 4-fold molar amount relative to the crude hexafluorobutadiene. _The hexafluorobutadiene containing 500 ppm of _C4F7H was fed to the extractive distillation step for separation of the two.

The outline of the flow is shown in FIG. 1 . The theoretical number of stages of the distillation column is 14 stages for the extractive distillation column T1 and 8 stages for the solvent recovery column T2. The operating pressure of the extractive distillation tower and the solvent recovery tower is 0.05MPaG (G refers to gauge pressure), and the temperature of the distillation device is 72.4°C for the extractive distillation tower and 75.1°C for the solvent recovery tower.

The material budget is shown in Table 2 below.

Comparative Example 1 The calculation was carried out when hexafluorobutadiene containing 500 ppm of C ₄ F ₇ H as an impurity was separated only by ordinary distillation without using an extractive distillation step.

It can be seen that in order to achieve the same product recovery rate as in Example 1 with a purity of 4N, a distillation column with a theoretical number of 120 stages is required.

According to the above, no matter what kind of solvent is used, the target purity of 99.99% or more (4N) can be achieved by extractive distillation with a surprisingly smaller equipment than ordinary distillation.

Example 2 Under the etching conditions of ICP (Inductive Coupled Plasma) discharge power 600W, bias power 200W, pressure 3mTorr (0.399Pa), electron density 8×10 ¹⁰ ~2 ×10 ¹¹ cm ^-3 , and electron temperature 5~7eV , using cyclic cC ₄ F ₈ (conventional product) and C ₄ F ₆ (structure CF ₂ =CFCF =CF ₂ ) produced in Reference Example 1, a SiO ₂ film with a thickness of about 1 μm was formed on the Si substrate, and then its The etching rates and selectivity ratios of the semiconductor substrate having the resist pattern with a hole diameter of 0.21 μm in etching are shown in Table 3 below.

C ₄ F ₆ (structure CF ₂ =CFCF=CF ₂ ) has higher selectivity than cC ₄ F ₈ both for electron beam drawing resist and for silicon.

T1‧‧‧Distillation Column T2‧‧‧Solvent Recovery Tower S11‧‧‧hexafluorobutadiene S14‧‧‧extraction solvent F11‧‧‧Composition

Fig. 1 shows an example of an apparatus for carrying out the separation method (the production method of hexafluorobutadiene) of the present invention.

Claims (7)

A method for producing hexafluorobutadiene, comprising the step of extracting and distilling a raw material composition comprising hexafluorobutadiene and an additional compound in the presence of an extraction solvent to reduce the concentration of the additional compound, wherein the additional compound is selected from the group consisting of eight At least one selected from the group consisting of fluoro-1-butene, octafluoro-2-butene and heptafluoro-2-butene. The production method according to claim 1, wherein the extraction solvent contains at least one compound selected from the group consisting of oxygen-containing hydrocarbons and halogen-containing hydrocarbons. A method for separating hexafluorobutadiene and at least one additional compound selected from the group consisting of octafluoro-1-butene, octafluoro-2-butene and heptafluoro-2-butene, comprising: The step of subjecting the composition comprising hexafluorobutadiene and the aforementioned additional compound to extractive distillation in the presence of an extraction solvent. The method of claim 3, wherein the extraction solvent comprises at least one compound selected from the group consisting of oxygen-containing hydrocarbons and halogen-containing hydrocarbons. A composition comprising hexafluorobutadiene and at least one additional compound selected from the group consisting of octafluoro-1-butene, octafluoro-2-butene and heptafluoro-2-butene The total amount of the aforementioned composition is set at 100 mol %, and the content of the aforementioned additional compound is less than 0.1 mol %. An azeotropic composition comprising hexafluorobutadiene and at least one additional compound selected from the group consisting of octafluoro-1-butene, octafluoro-2-butene and heptafluoro-2-butene compound. The composition of claim 5 or 6, which is a composition for etching gas, refrigerant, heat transfer medium, foaming agent or resin monomer.

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